1. Field of the Invention
The present invention relates to an image forming apparatus and a cartridge attachable/detachable to/from the image forming apparatus.
The term image forming apparatus refers to an apparatus for forming an image on a recording medium. For example, an electrophotographic copying machine, an electrophotographic printer (such as a light emitting device (LED) printer and a laser beam printer), and an electrophotographic facsimile apparatus which use an electrophotographic image forming process are included in the image forming apparatus.
The term recording medium refers to a medium on which an image is formed. For example, a recording sheet and an overhead projector (OHP) sheet are included in the recording medium.
The term cartridge refers to a cartridge in which a part of a mechanism used in the image forming apparatus is made attachable/detachable from the main assembly of the image forming apparatus.
2. Description of the Related Art
Now, an image forming apparatus usually employs a process cartridge system in which an electrophotographic photosensitive member and a process unit acting thereon are integrated into a cartridge attachable/detachable to/from the main assembly of the image forming apparatus. The process cartridge system is useful for improving operability of the image forming apparatus because a user can perform maintenance of the image forming apparatus.
A process cartridge is formed of a cleaning unit and a developing unit. The cleaning unit includes a cleaning member for cleaning an electrophotographic photosensitive drum acting as an image bearing member and the surface thereof. The developing unit includes a developing roller for supplying developer to the electrophotographic photosensitive drum and a developer storage unit for storing developer.
Meanwhile, a developer replenishment system is known as one of the process cartridge system. The system is configured in such a manner that the developer replenishment opening of a developer replenishment cartridge is connected with the developer acceptance opening of the process cartridge to replenish developer from the developer replenishment cartridge to the process cartridge.
In the developer replenishment system, if a new developer replenished from the developer replenishment cartridge is non-uniformly mixed with an old developer in the developing unit, harmful effects on images may occur. For this reason, the process cartridge of the developer replenishment system is provided with the following configuration (refer to FIG. 4 in Japanese Patent Application Laid-Open No. 2010-014890).
The development unit is divided into a development portion and a developer storage portion. The development portion and the developer storage portion are connected with each other through openings provided at both ends in the direction of the rotation axis of a developer photosensitive drum (hereinafter referred to as “longitudinal direction”).
Each of the development portion and the developer storage portion is provided with a screw acting as a developer conveyance member for conveying a developer and sheet member acting as a developer stirring member. The developer conveyance member and the developer stirring member convey the developer in the longitudinal direction. The developer is thus circulated in the development unit to uniformly mix a new and an old developer therein.
In general, an unused process cartridge is filled with a predetermined amount of developer. The developer in the developer storage portion of the unused process cartridge is sometimes pressed and coagulated by vibration generated when the developer is transported from a manufacture place to a user.
In particular, if the longitudinal direction of the process cartridge is oriented in parallel with the vertical direction and the downstream side in the conveyance direction of the developer conveyance member is oriented downward during the transportation, the developer is sometimes accumulated on the downstream side in the conveyance direction of the developer conveyance member and coagulated.
In this state, when driving force is transmitted in the image forming apparatus, the developer conveyance member is rotated to convey the developer and the coagulated developer is further pressed on the downstream side in the conveyance direction. The load torque of the developer conveyance member may probably be increased.
Japanese Patent Application Laid-Open No. 11-160985 discusses a configuration, as a solution for the above problem, in which a clutch is provided on a drive gear train of the developer stirring member and the developer conveyance member as illustrated in FIG. 1 thereof.
The above configuration is such that, if the developer stirring member and the developer conveyance member are driven by the same drive source and the drive source is overloaded, the rotation of the developer conveyance member is stopped and only the developer stirring member is rotated.